linux-kernel - [ 076/108] timekeeping: Fix CLOCK_MONOTONIC inconsistency during leapsecond

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Message-Id: <20120723010703.011762368@decadent.org.uk>
Date:	Mon, 23 Jul 2012 02:08:07 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, John Stultz <john.stultz@...aro.org>,
	Richard Cochran <richardcochran@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	John Stultz <johnstul@...ibm.com>
Subject: [ 076/108] timekeeping: Fix CLOCK_MONOTONIC inconsistency during leapsecond

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: John Stultz <john.stultz@...aro.org>

This is a backport of fad0c66c4bb836d57a5f125ecd38bed653ca863a
which resolves a bug the previous commit.

Commit 6b43ae8a61 (ntp: Fix leap-second hrtimer livelock) broke the
leapsecond update of CLOCK_MONOTONIC. The missing leapsecond update to
wall_to_monotonic causes discontinuities in CLOCK_MONOTONIC.

Adjust wall_to_monotonic when NTP inserted a leapsecond.

Reported-by: Richard Cochran <richardcochran@...il.com>
Signed-off-by: John Stultz <john.stultz@...aro.org>
Tested-by: Richard Cochran <richardcochran@...il.com>
Link: http://lkml.kernel.org/r/1338400497-12420-1-git-send-email-john.stultz@linaro.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: Prarit Bhargava <prarit@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Linux Kernel <linux-kernel@...r.kernel.org>
Signed-off-by: John Stultz <johnstul@...ibm.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/time/timekeeping.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 4780a7d..5c9b67e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -938,6 +938,7 @@ static cycle_t logarithmic_accumulation(cycle_t offset, int shift)
 		xtime.tv_sec++;
 		leap = second_overflow(xtime.tv_sec);
 		xtime.tv_sec += leap;
+		wall_to_monotonic.tv_sec -= leap;
 	}
 
 	/* Accumulate raw time */
@@ -1048,7 +1049,7 @@ static void update_wall_time(void)
 		xtime.tv_sec++;
 		leap = second_overflow(xtime.tv_sec);
 		xtime.tv_sec += leap;
-
+		wall_to_monotonic.tv_sec -= leap;
 	}
 
 	/* check to see if there is a new clocksource to use */


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